A Single 808 nm Near-Infrared Light-Mediated Multiple Imaging and Photodynamic Therapy Based on Titania Coupled Upconversion Nanoparticles

To solve the issue of limited penetration depth and overheating of the excited 980 nm near-infrared (NIR) light, and unstable and insufficient loading amount of photosensitizers (PSs) in photodynamic therapy (PDT), we have constructed a well-defined core–shell structured NaGdF4:Yb/Tm@NaGdF4:Yb@NaNdF4:Yb@NaGdF4@mSiO2@TiO2 (UCNPs@mSiO2@TiO2) nanocomposite by coating a layer of TiO2 PSs/photocatalyst on an effective 808 nm-to-UV/visible upconversion luminescent (UCL) core to achieve simultaneous multiple bioimaging and efficient PDT. The design of quenching-shield layer can eliminate the back energy transfer from activator Tm3+ to sensitized Nd3+, thus significantly improving the UCL emission. The high surface area of mesoporous silica-coated UCNPs facilitates the stable and high loading amount of anatase TiO2. In vivo results indicate that 808 nm NIR light-mediated PDT using UCNPs@mSiO2@TiO2 as photosensitizers shows much higher antitumor efficacy than those with 980 nm and UV irradiations due to the higher tissue penetration depth. Meanwhile, the platform itself as an imaging nanoprobe endows the sample with multiple imaging (UCL/CT/MRI) properties. Our work makes great progress toward the integrity of diagnosis and PDT induced by a single 808 nm NIR light.